A. Field of the Invention
The present invention relates to improvements in equipment for direct heat treating a hot rolled steel wire rod by taking advantage of the heat retained in the rod from the hot rolling, and more particularly, to multi-purpose in-line direct heat treating equipment for hot-rolled steel wire rod wherein wire rod the quality of which is equal to that of conventional lead-patented or air-patented wire rod can be manufactured in a stable and assured manner, and a direct solution treatment can also be conducted on an austenitic stainless steel wire rod.
B. Description of the Prior Art
A conventional high carbon steel wire rod produced by hot rolling has heretofore been subjected to air-patenting (referred to as AP hereinafter) and leat-patenting (referred to as LP hereinafter) prior to cold working, such as wire drawing, with a view to enhancing drawability, strength and toughness. Recently, there has been carried out a direct heat treatment (referred to as DP hereinafter) in which heat retained in the wire rod from the hot rolling is fully utilized. However, while various methods of DP heretofore conducted or proposed can manufacture a wire rod the quality of which is almost equal to that resulting from AP, as a matter of fact, the quality has not reached the level where a rod the quality of which is equal to that resulting from LP can be obtained.
Miscellaneous methods for heat treating the wire rod in the course of cooling immediately after the hot rolling have frequently been effected, and miscellaneous equipment for carrying out these methods is also widely known. For instance, Japan Patent Publication No. SHO 46-6690 (1971) discloses a method and apparatus for cooling non-concentric opened coils or rings of wire rod, and Japan Open-laid Patent No. SHO 52-111810 (1977) discloses an apparatus for carrying out controlled cooling of wire, particularly, steel wire.
However, in the widely adopted conventional methods of the above type, the most prevalent cooling process is the process of air-cooling the wire rod the coils or rings of which have been opened as wide as possible. In this method of cooling, however, the range of cooling capacity is so narrow that both uniformity and rapidity of cooling required for a high carbon steel wire rod are not achieved, and hence this type of cooling process results in inadequate cooling. Recently, wire rod has tended to have high tensile strength and a large diameter, and particularly where uniform quality of wire rod is in much demand, the effect of heat treatment by means of air-patenting is not fully achieved because the air-cooling method lacks cooling capacity. Furthermore, in air-cooling, of stainless steel wire rod, a solution treatment cannot be carried out because the temperature of the start of cooling is low and the cooling rate is slow.